Heatstake

ABSTRACT

A heatstake for fastening a workpiece includes a base portion ( 12 ) having at least one shaft portion ( 22 ). A central passage extends though the shaft portion from its leading end ( 28 ) to the base portion. A plurality of slots ( 22 ) are disposed about an outer surface ( 34 ) of the shaft portion ( 22 ). The plurality of slots ( 32 ) have a predefined angular separation. Preferably, the plurality of slots ( 32 ) disposed about the outer surface of the shaft portion form a heatstake having multiple fastening portions. The multiple fastening portions are adapted to form a geometric flower shape for increasing the fastening strength of a heatstake when staked.

TECHNICAL FIELD

The present invention relates to a fastener, and in particular to aheatstake fastener that has multiple fastening portions for fastening aworkpiece.

BACKGROUND OF THE INVENTION

Conventional heatstakes normally employ a base portion having a shaftportion that extends through a passage of a workpiece. When the shaftportion is heat-staked, the result is a deformed fastener about thepassage and fastening surface of the workpiece. The deformed shaft forthis conventional heatstake does not provide a uniform, consistent, orcompletely fastened workpiece during the staking operation. The shaftportion deforms freely in an uncontrolled fashion and is completelygoverned by the staking device. If the shaft is not heat-stakedproperly, only a portion of the deformed shaft will contact thefastening surface, resulting in an insufficient fastener. Further, theshaft portion may be staked entirely through the workpiece passage andmay never contact the fastening surface, resulting in the absence of afastener for the workpiece.

SUMMARY OF THE INVENTION

The inventor of the present invention has recognized that the shaftportion of conventional heatstakes deform freely in an uncontrolledfashion. To this end, the inventor has developed a heatstake having ashaft portion that can be staked in a controlled fashion. Thus, anobject of the present invention is to provide a heatstake that resultsin a uniform, consistent, and generally fastened workpiece.

The heatstake comprises a base portion having at least one shaftportion. The shaft portion is defined by a leading end and a centralpassage that extends through the shaft portion. The central passage isformed by an opening at the leading end. A plurality of slots aredisposed about an outer surface of the shaft portion. The plurality ofslots have a predefined angular separation. The plurality of slotsdisposed about the outer surface of the shaft portion form a heatstakehaving multiple fastening portions, which when staked, allow theformation a uniform, consistent, and completely fastened workpiece.

BRIEF DESCRIPTION OF THE DRAWINGS

The present invention will now be described, by way of example, withreference to the accompanying drawings, in which:

FIG. 1 is a perspective view of the heatstake;

FIG. 2 is a cross-sectional view of the heatstake of FIG. 1;

FIG. 3 a is a top view of the heatstake of FIG. 1;

FIG. 3 b is a top view of an alternate embodiment of the heatstake ofFIG. 1;

FIG. 4 a is a top view of a staked heatstake of FIG. 3 a;

FIG. 4 b is a top view of an alternate embodiment of a staked heatstakeaccording to FIG. 3 b;

FIG. 5 is a perspective view of an alternate embodiment of theheatstake;

FIG. 6 is a cross-sectional view of the heatstake of FIG. 5;

FIG. 7 is a top view of the heatstake of FIG. 5.

DESCRIPTION OF THE PREFERRED EMBODIMENT

The present invention is directed to a heatstake having a base and shaftportion that allows the formation of a uniform, consistent, andgenerally fastened workpiece. FIG. 1 shows the heatstake, showngenerally at 10, before being staked. The term “staked” is generallyapplied to a staking operation that includes any one of a plurality offastening methods known in the art, such as conventional welding,ultrasonic welding, and the like. Preferably, the heatstake is made of arigid plastic material such as a polypropylene, nylon,Acrylnitril-Butadien-Styrol-Copolymere (ABS), and the like. It will beappreciated that the invention is not limited by the type of material,and that the invention can be practiced with any suitable deformablematerial that can allow the user to stake the heatstake 10 in a uniformand consistent fashion.

Referring now to FIGS. 1-3 a, the heatstake is shown having a baseportion 12 and a shaft portion 14. The shaft portion 14 extends througha passage 16 of a workpiece 18. The shaft portion 14 includes a first orinner shaft portion 20 and a second or outer shaft portion 22. The firstshaft portion 20 is defined by a first leading end 24 and a firstcentral passage 26. The second shaft portion 22 is defined by a secondleading end 28 and a second central passage 30. The first shaft portion20 is generally concentrically disposed about the second central passage30 of the second shaft portion 22 to form a dual heatstakeconfiguration. The first shaft portion 20 is further defined as tohaving an outer diameter D1 that is less than the inner diameter D2 ofthe second shaft portion 22 FIG. 3 a). The first and second centralpassages 26, 30 generally concentrically extend through the first 20 andsecond shaft portion 22 from the first and second leading ends 24, 28,respectively. Preferably, the first shaft portion 20 has a length, L1,that is greater than a length, L2, of the second shaft portion 22 (FIG.2). Because the length, L1, of the first shaft portion 20 is greaterthan the length L2 of the second shaft portion 22, the leading end 24 ofthe first shaft portion 20 comes into contact with the staking device(not shown) before the leading end 28 of the second shaft portion 22.

One aspect of the invention is that a plurality of slots 32 are disposedthrough an outer surface 34 of the second shaft portion 22. In thisembodiment, the plurality of slots 32 have an angular separation, θ(FIG. 3 a). The user may selectively design the amount of slots 32needed for a particular heatstake design. Each slot 32 forms a fasteningportion 36 that securely contacts a fastening surface 38 of a workpiece18 when the heatstake 10 is staked. The slots 32 may be positioned so asto define the predefined angular separation θ having substantiallyequivalent angles that help ensure that the shaft portion 14, whenstaked, will securely and positively engage the fastening surface 38.

For example, the heatstake 10 shown in FIG. 3 a includes three slots 32having an angular separation, θ, of approximately 120° . When theheatstake 10 is staked, the deformed heatstake fastens to the workpiece18 with three fastening portions 36 that securely and positively engagethe fastening surface 38 of the workpiece 18. However, it will beappreciated that the invention is not limited to having only three slots32 with an angular separation, θ, of approximately 120° . The inventioncan be practiced with any suitable number of slots that allow the userto stake the heatstake in any desired fashion. For example, theheatstake may have eight slots with an angular separation, θ, ofapproximately 45° that when staked forms eight fastening portions 36. Ingeneral, the angle separation, θ, between the slots 32 is defined by thefollowing expression: θ=(360/N) degrees, where N is the number of slots.The expression for θgenerally defines an equivalent angular separationfor each slot 32. However, it will be appreciated that the aboveexpression for θ may not necessarily limit the heatstake 10 from usingonly equivalent angles. The slots 32 may be designed with any angulardisplacement, which may not necessarily include equivalent angles, θ,that will adequately fasten the heatstake to the workpiece.

The invention is not limited by the number of outer shaft portions. Forexample, in an alternate embodiment to the heatstake design shown inFIG. 3 b, a heatstake 10 a may further comprise a third shaft portion 22a including three fastening portions 36 a defined by three slots 32 ahaving an angular displacement, θa, of approximately 120° . The thirdshaft portion 22 a is further defined as to having an inner diameter D3that is greater than the outer diameter opposite the inner diameter D2of the second shaft portion 22. The slots 32 a are centrally positionedopposite that of fastening portions 36 of the second shaft portion 22.The third shaft portion 22 a may also have a length (not shown) that isless than the length, L2, of the second shaft portion 22. When theheatstake 10 a is staked, the deformed heatstake fastens to theworkpiece 18 with three additional fastening portions 36 a thatcomplements the fastening portions 36 of the second shaft portion 22.The fastening portions 36 and 36 a securely and positively engage thefastening surface 38 of the workpiece 18. However, it will beappreciated that the invention is not limited to having only three slots32 a with an angular separation, θa, of approximately 120° . Asexplained above, the invention can be practiced with any suitable numberof slots that allow the user to stake the heatstake in any desiredfashion with a variety of displacement angles, θa.

Referring back to the original embodiment shown in FIGS. 1-3 a, FIG. 2shows a cross-sectional view of the heatstake 10 before it is staked.Hidden lines, H, show the first and second central passages 26, 30generally concentrically extending through the first and second shaftportions 20, 22 about a central axis, V. The passage 26 extends from itsleading end 24 to the base portion 12. Although the passage 26 is notshown extending through the base portion 12, the passage 26 may extendthrough the base portion 12 to provide an opening (not shown) in anopposing surface 40. The slots 32 of the second shaft portion 22 have alength, L3, defined from the second leading end 28 and extend proximatethe fastening surface 38 of the workpiece 18. It will be appreciatedthat the length, such as the length L3, may extend to any desired lengthof the second shaft portion 22, or a length less than L2.

The staking operation is performed by centrally inserting a stakingdevice (not shown) into the first central passage 26 about the firstleading end 24. The staking operation causes the first shaft portion 20to deform vertically downward and radially outward about the verticalaxis, V, against the second shaft portion 22 having the plurality ofslots 32 with the predefined angular separation, θ. In addition, eachfastening portion 36 of the second shaft portion 22 deforms verticallydownward and radially outward about the vertical axis, V, toward thefastening surface 38 of a workpiece 18. Because the first shaft portion20 has a generally solid, cylindrical outer surface 40, the fasteningportions 36 that deform radially outward from the vertical axis, V,apply a substantially uniform and continuous pressure to the fasteningportions 36. When the shaft 14 is deformed in this fashion, thefastening portions 36 are deformed uniformly and consistently, therebyproviding a generally fastened workpiece 18 about the fastening surface38.

As seen in FIG. 4 a, the deformed heatstake 10 having three slots 32forms a geometric configuration of a deformed first shaft portion 20 ina generally circular shape having a second shaft portion 22 deformed inthe shape of a rosette or flower 44 with three pedals 46 separatedapproximately 120° apart. FIG. 4 b shows the deformed heatstake 10 aaccording to the alternate heatstake design of FIG. 3 b. As shown inFIG. 4 b, the second shaft portion 22 and third shaft portion 22 a aredeformed in the shape of a rosette or flower 44 with two series of threepedals 46, 46 a, separated approximately 1200 apart, respectively. Theflowering pattern 44 a shown in FIG. 4 b is similar to the floweringpattern 44 shown in FIG. 4 a, except that the passage 16 (shown bydashed lines), formed in the workpiece 18 is completely covered by thepedals 46 a. Thus, one advantage of the alternate embodiment shown inFIGS. 3 b, 4 b is that the third shaft portion 22 a provides anincreased fastening strength as compared to the embodiment shown inFIGS. 3 a, 4 a, because of the increase in the amount of surface area,provided by pedals 46 a, contacting the fastening surface 38 by theheatstake 10 a.

The shape of each pedal 46, 46 a is controlled by a combination of anumber of factors that include inherent characteristics of the heatstake10, 10 a, as well as the conditions of the staking process. Inherentcharacteristics that result in the ‘mushrooming’ or deformation of eachpedal 46, 46 a includes the material used in the construction of theheatstake 10, 10 a, as well as the radial thickness R1 and R2 of thefirst and second shaft portions 20, 22, respectively (FIG. 1). If theradial thickness R2 extends to a sufficient thickness, the volume ofmaterial used for the second shaft portion 22 will also increase, whichresults in larger flowered-out pedals 46 that will completely engage thepassage 16. Thus, the passage 16 may also be completely covered by usingthe first and second shaft portions 20, 22 of the embodiment shown inFIG. 3 a. During the staking process, conditions, such as the amount ofheat and the time that the heat is applied to the heatstake 10, 10 a,also generally determines the ‘mushrooming’ or deformation of each pedal46, 46 a.

The deformed first shaft portion 20 for both embodiments shown in FIGS.4 a and 4 b fastens to the workpiece 18 as each pedal 46, 46 a increasesthe fastening strength of the deformed heatstake 10 to the fasteningsurface 38. However, the invention is not limited to having only threeslots 32, 32 a. For example, as shown above, the heatstake 10, 10 a mayhave any desired number of slots 32, 32 a designed with any angulardisplacement, which may not necessarily include equivalent angles, θ,that will adequately fasten the heatstake to the workpiece. It will beappreciated that the number of slots 32, 32 a determines the number offastening portions 36, 36 a, which in turn determines the number ofpedals 46, 46 a on the deformed heatstake 10, 10 a, respectively.

FIG. 5 shows an alternate embodiment of a heatstake 100 according to theinvention. In general, the heatstake 100 is substantially identical tothe heatstake 10, except that the heatstake 100 does not include thefirst shaft portion 20. The heatstake 100 includes a base portion 112and a single shaft portion 114. The shaft portion 114 extends through apassage 116 of a workpiece 118. The shaft portion 114 is defined by aleading end 120 and a central passage 122. The first shaft portion isfurther defined as to having an outer diameter D4 and an inner diameterD5 that is less than the outer diameter D4 (FIG. 7). A plurality ofslots 124 are disposed about an outer surface 126 of the shaft portion114.

Like the first embodiment shown above, the plurality of slots 124 have aangular separation, θ (FIG. 7). The user may selectively design theamount of slots 124 needed for the present embodiment having a singleshaft portion 114 in the heatstake 100. Each slot 124 forms a fasteningportion 128 that securely contacts a fastening surface 130 of aworkpiece 118 when the heatstake 100 is staked. The slots 124 may bepositioned so as to define the predefined angular separation θ havingsubstantively equivalent angles that help ensure that the shaft portion114, when staked, will generally and positively engage the fasteningsurface 130. For example, the heatstake 100 shown in FIG. 7 includesthree slots 124 having an angular separation, θ, of approximately 120° .When the heatstake 100 is staked, the deformed heatstake fastens to theworkpiece 118 with three fastening portions 128 that securely andpositively engage surface 130 of the workpiece 118. However, it will beappreciated that the invention is not limited to having only three slots124 with an angular separation, θ, of approximately 120° . The inventioncan be practiced with any suitable number of slots that allow the userto stake the heatstake in any desired fashion. For example, theheatstake may have eight slots with an angular separation, θ, ofapproximately 450 that when staked forms eight fastening portions 128.

FIG. 6 shows a cross-sectional view of the heatstake 100 before it isstaked. As discussed above, hidden lines H show the central passage 122extending through the shaft portion 114 about central axis V. Althoughthe passage 122 is not shown extending through the base portion 112, thepassage 122 may extend through the base portion 112 to provide anopening (not shown) in an opposing surface 132. The slots 124 of theshaft portion 114 have a length, L4, defined from the leading end 120and extend proximate the fastening surface 130 of the workpiece 118. Itwill be appreciated that the length L4 may extend to any desired length,such as the length of the shaft portion 114, or a length less than L4.

The staking operation is performed by centrally inserting a stakingdevice (not shown) into the first central passage 122 about the leadingend 120. The staking operation causes the shaft portion 114 to deformvertically downward and radially outward about the vertical axis, V, sothat the fastening portions 128 defined by the plurality of slots 124with the predefined angular separation, θ, generally and positivelyengage the fastening surface 130 of the workpiece 118. When the shaft114 is deformed in this fashion, the fastening portions 128 are deformeduniformly and consistently, thereby providing a generally fastenedworkpiece 118 about the fastening surface 130.

The end result of the staking operation is a deformed heatstake 100 thatforms a geometric configuration of a rosette or flower with three pedalsthat are separated approximately 120° apart. The deformed shaft portion114 fastens to the workpiece 118 with each pedal. As discussed above,the invention is not limited to having only three slots with an angularseparation of approximately 120° . For example, the deformed heatstake100 may have any desired number of slots 124 that will adequately fastenthe heatstake to the workpiece.

Another advantage of the present invention is the ability to design andform a heatstake on a workpiece through injection molding. The heatstakedescribed above can be injection molded onto a workpiece before theperformance of a staling operation. The ability to provide a heatstakethat can be injection molded onto a workpiece before the implementationof a staking process can allow for easier and faster assembly.

It will be appreciated that there are many different ways in which tomaintain a uniform, consistent, and complete fastener other than theembodiments shown for heatstakes 10, 10 a, and 100. Any differentcombination, addition, or withdrawal of the amount of stakes, slots, orangular displacement θ can be used to improve upon the fasteningstrength or deformation consistency disclosed herein. It should beunderstood that the aforementioned and other various alternatives to theembodiments of the invention described herein may be employed inpracticing the invention. It is intended that the following claimsdefine the scope of the invention and that the method and apparatuswithin the scope of these claims and their equivalents be coveredthereby.

1. A heatstake for fastening a workpiece, comprising: a base portion;first and second concentrically disposed shaft portions the first shaftportion having a leading end and a length greater than a length of thesecond shaft portion; a central passage extending through the first andsecond shaft portions; and a plurality of slots disposed about an outersurface of the second shaft portion having a predefined angularseparation, the plurality of slots defining a plurality of fasteningportions when the second shaft portion is deformed, wherein the firstshaft portion applies pressure against the fastening portions of thesecond shaft portion when the first shaft portion is deformed.
 2. Theheatstake according to claim 1, wherein the plurality of slots comprisesat least three slots.
 3. The heatstake according to claim 2, wherein thepredefined angular separation is approximately 120 degrees.
 4. Theheatstake according to claim 1, wherein the fastening portions of thesecond shaft portion form a geometric configuration in the form of arosette or flower shape.
 5. A heatstake for fastening a workpiece,comprising: a base portion; a first shaft portion including a firstleading end and a first central passage; a second shaft portionincluding a second leading end, a second central passage, and aplurality of slots disposed about an outer surface having a predefinedangular separation, the plurality of slots defining a plurality offastening portions when the second shaft portion is deformed, whereinthe first shaft portion is generally concentrically disposed about thesecond central passage of the second shaft portion such that the firstshaft portion applies pressure against the fastening portions of thesecond shaft portion when the first shaft portion is deformed.
 6. Theheatstake according to claim 5, wherein the first shaft portion has anouter diameter less than an inner diameter of the second shaft portion.7. The heatstake according to claim 5, wherein the plurality of slotscomprises at least three slots.
 8. The heatstake according to claim 7,wherein the predefined angular separation is approximately 120 degrees.9. A method of deforming a heatstake in a controlled fashion, theheatstake comprising a base portion, first and second concentricallydisposed shaft portions, the first shaft portion having a leading endand a length greater than the second shaft portion a central passageextending through the first and second shaft portions, and a pluralityof slots disposed about an outer surface of the second shaft portionhaving a predefined angular separation, the plurality of slots defininga plurality of fastening portions when the second shaft portion isdeformed, the method comprising the steps of: deforming the first shaftportion vertically downward and radially outward about a vertical axisof the first shaft portion such that the first shaft portion appliespressure against the fastening portions of the second shaft portion topositively engage a workpiece.
 10. The method according to claim 9,wherein the fastening portions define a geometric configuration in theform of a rosette or flower shape.